Fuse construction



Oct. 30, 1956 N. BAENZIGER 2,769,059

FUSE CONSTRUCTION Filed May 10, 1955 United States Patent "ice FUSECONSTRUCTION Leonard N. Baenziger, Pawtucket, R. 1., assignor to RoyalElectric Company, Inc., Westerly, R. I., a corporation of Rhode IslandThe present invention relates to a novel construction for a circuitprotective fuse. The type of fuse to which this invention particularlyrelates is one which is adapted not only immediately to protect thecircuit in which it is connected from extreme current overloads, such asmight be caused by a short circuit or the like, but also to pro tect thecircuit against minor overloads which persist beyond a predeterminedperiod of time.

Fuses of this particular type generally comprise a conductive linkformed of readily fusible material, the link itself therefore beingself-destructive so as to open the circuit through the fuse quitepromptly upon the occurrence of heavy overloads. A portion of theelectrical circuit through the fuse is additionally defined by amaterial having a fairly low melting point, that material serving tophysically and electrically connect two elemerits together and beingheld under tension in juxtaposition to a current carrying element havingan appreciable electrical resistance. Slight overloads will cause theelement of high electrical resistance to heat up sufficiently to melt orsoften the connecting material, and because of the tension thereon thejunction defined thereby will separate provided that the heating effectof the high resistive element continues at a sufficient magnitude for asufficient period of time. In this manner if a slight overload shouldoccur the circuit through the fuse will not be immediately opened, butif that slight overload should continue for an excessive period of time,the circuit will be opened. The period of time will of course varydepending upon the magnitude of the overload, the greater the currentthe greater the heat developed in the element having a high electricalresistance, and consequently the sooner will the junction material besoftened or melted.

The fuse structure of the present invention provides for a simplifiedyet positively acting arrangement of parts in a device of thischaracter. In particular it provides for a structure in which, when thecircuit has been interrupted for either of the reasons above set forth,the major structural portions of the fuse may be reused, it beingnecessary to replace only one inexpensive sub-assembly therein and thefuse construction being such as to facilitate such replacement. To thisend the elements which enable the fuse to function as described areassembled into a unitary structure readily removable as such from thehousing, that structure in turn being disassemblable and the elementsthereof through which current is adapted to pass comprising a sub-unitinsertable as such into the aforementioned unitary structure. Thatsub-unit comprises a pair of conductors, preferably fusible in nature,between which a conductive and preferably heat absorptive elementextends, the element being connected to the conductors by materialhaving a relatively low softening point. The remainder of the fusestructure, apart from the housing, includes supports on which theconductors are mounted in such a way that the conductive elementextending therebetween is free to move in a given direction. Thestructure carries biasing means Patented Oct. 30, 1956 active on thatconductive element so as to tend to urge it in the direction in which itis free to move, the conductive element normally being prevented frommovement in that direction by the material of low softening point whichconnects it to the ends of the conductors. The biasing means ispermanently associated with the supporting structure, so that even afterit has been operative, for example, to separate the conductive elementfrom the conductors when a small overload has persisted for an excessiveperiod of time, said biasing means still remains secured to the supportand ready to perform its functions anew after a new sub-unit ofconductors and The biasing means not only acts to positively separatethe conductive element from the conductors when the material of lowsoftening point is sufficiently heated, but

also serves to tension the fusible conductors themselves. As a resultwhen an excessive overload causes a conductor to fuse, the biasing meanswill quickly separate the conductor at the fused area, thus providingfor prompt breaking of the current through the fuse, minimizing arcing,and minimizing the generation of gases within the fuse housing.

To the accomplishment of the above, and to such other objects as mayhereinafter appear, the present invention relates to a fuse constructionas defined in the appended claims and as described in thisspecification, taken together with the accompanying drawings, in which:

Fig. 1 is a cross sectional view of a fuse made according to the presentinvention and showing the fuse in normal condition;

Fig. 2 is a view similar to Fig. l but showing the manner in which thecircuit through the fuse is broken in the event of an excessiveoverload; and

Fig. 3 is a view similar to Fig. l but showing the manner in which thecircuit through the fuse is broken in the event that a moderate overloadpersists for an excessive period of time.

The fuse comprises a tubular housing 2, preferably formed of someinsulating material and which may be transparent or not, as desired, theends 4 of the housing being externally threaded. Caps 6 are adapted tothreadedly engage the portions 4 of the housing 2 so as to close theends of the latter. These caps are provided with central openings 8through which conductive blades 16 extend, the portions of those blades10 which extend beyond the caps 6 constituting the means by whichelectrical connection to the fuse is made. Bafile washers 12 bearagainst the inner surfaces of the caps 6 and snugly encompass thoseportions of the blades 10 which pass therethrough, the baffle washers 12obstructing free passage of gas from the interior of the housing 2 tothe exterior thereof. Copper washers 14 abut the inner surfaces of thebaffle Washers 12 and function to absorb the heat which may be producedwhen gases are generated within the housing 2.

Mounted between the copper washers 14 is a strut 16 formed of somesuitable insulative material, the strut 16 being secured to the inwardlyprojecting portions of the blades 10 by means of bolts 18. The strut 16is provided with a vertical opening 20 appropriately positioned alongits length through which a pin 22 is slidable, that pin having anenlarged head 24 above the upper surface of the strut 16. A leaf spring26 is secured to the strut 16 by means of rivet or eyelet 28, and thetip 30 of the leaf spring 26 overlies of the head 24 of the button 22.As may be seen from Figs. 2 and 3, the spring 26 tends to urge the pin22 downwardly until its head 24 rests on the upper surface of the strut16. The fact that the pin head 24 is larger than the opening 22 preventsthe pin 22 from separating from the strut 16 under the infiuence of thespring 26.

Secured beneath the inwardly extending portions of the blades by thebolts 18 are a pair of supports 32 substantially parallel to the strut.16, the tips '34 of the supports 32 being spaced from one another so:as to define an opening beneath the opening 20 in the strut 16. A pairof conductors 36 are mounted on the supports 32, also by means of thebolts 18, the outer ends of the conductors engaging the inner ends ofthe plates 10 and the inner ends 38 of the conductors extending towardone another beyond the tips 34 of the supports 32, a space being definedbetween the inner conductor ends 38 beneath the opening 20 in the strut16. One or both of the conductors .36 is preferably formed of fusiblematerial of a type well known in the fuse art, and certain portions ofthe body thereof may be weakened or cut away in order to ensure thatfusing will take place, when an excessive overload is present, at thoseweakened or cut-away areas.

Nuts 19 and washers 21 serve to maintain all of the fuse parts exceptthe housing 2, caps 6 and washers 12 and 14 connected together to definea unitary structure.

A conductive element 40 is positioned between the tips 34 of thesupports 32 directly beneath the pin 22 and extends between and isconnected to the inner ends 38 of the conductors 36 at their lowersurfaces by means of heat sensitive material vsuch as low melting pointsolder 42 the composition of which is well known to those in the fuseart. The conductive element 40 is of asize such as to be freely passablebetween the tips 34 of the supports 32. When it is held to the lowersurfaces of the inner conductor ends 38 it is engaged by the tip 44 ofthe pin 22 which extends below the strut 16, forcing the pin 22 upwardlyand flexing the spring 26, as shown in Fig. l. The pin 22, as urgeddownwardly by the spring 26, biases the heat absorption pad 40downwardly and at the same time tensions the conductors 36, andparticularly those portions thereof which extend beyond the tips 34 ofthe supports 32. The conductive element 40 is preferably formed ofappropriate material and provided with a mass such as to function as aheat absorption pad the temperature of which will rise when heat isgenerated therein or in the conductors 36, thereby heating the lowmelting point solder 42.

Should an excessive current overload pass through the fuse (See Fig. 2),one or both of the conductors 36 will quickly fuse, at the weakened orcut-away areas thereof if such are provided. In that event, as shown inFig. 2, the pin 22 will be moved downwardly by the spring 26 so as toseparate the two portions of the fused conductor 36, thus providing fora quick break of the circuit through the fuse, minimizing thepossibility of arcing, and minimizing the generation of gases attendantupon the fusing of the material of which the conductor 36 is formed.Some such gases may well be produced, but the baffle washers 14 willpermit the escape thereof only very slowly, thus eliminating anypossibility of danger.

Should a. slight current overload persist for an excessive period oftime (See Fig. 3), the passage of current through the conductors 36 andthe conductive element 40 will cause the temperature .of the low meltingpoint solder 42 to rise. The rate at which that temperature will risewill be determined in part by the magnitude of the current and in partby the electrical resistance of the conductors 36 and the conductiveelement 40. The temperature of the low melting point solder 42 will bedetermined in'part by the rate at which heat is generated, and in partby the heat absorptive capacity of the element 40. Eventually, if theoverload .persists long enough, the solder 42 will be sufficientlysoftened so that the action of the pin 22 in tending .to force theelement 4.0 downwardly will overcome the retentive action of the solder42. When that occurs the element 4i) will be positively snappeddownwardly, separated from the inner conductor ends 38, and permitted tofall to the bottom of the housing, all this occurring quite rapidly soas to produce an abrupt interruption of the current through the fuse.

Whether the current through the fuse is interrupted because of thepresence of an excessive overload (Fig. 2) or because of the persistenceof a slight overload for an excessive period of time (Fig. 3), the bulkof the fuse structure may nevertheless be reused upon the replacement ofthe sub-unit defined by the conductors 36 and the conductive element 40connected to the inner conductor ends 38 by low melting point solder 42.This replacement may very readily be effected by removing one of thecaps 6, sliding the fuse unit out of the housing 2, removing the nuts 19and washers 21 from the bolts 18, removing the supports 32 from the nuts13, extracting whatever portions of the conductors 36 and conductiveelement 40 may remain, replacing them with a new subunit of conductors36 and conductive element 46, replacing the supports 32, reapplying thenuts 19 and washers 21, reinserting the unitary fuse structure into thehousing 2, and replacing the cap 6. When the new conductor-conductiveelement sub-unit is put in place the pin 22 will be lifted and thespring 26 will be flexed to its position shown in Fig. 1, andconsequently the fuse will again be ready for use. The operatingmechanism of the fuse, apart from the electrical and heat sensitiveparts thereof, may be reused time and again, and the only replacementpart needed is the relatively inexpensive sub-unit defined by theconductors 36 and the element 40.

While but a single embodiment of the present invention has been heredisclosed, it will be apparent that many variations may be made therein,all within the scope of the present invention as defined by thefollowing claims.

I claim:

1. A fuse construction comprising a housing and a unitary structureremovable from and insertable into said housing as such, said unitarystructure comprising, a pair of conductors the ends of which areseparated from one another, a support on which said conductors aremounted and fixed against movement in a given direction, a conductiveelement extending between said conductors and connected to the endsthereof by a heat sensitive substance, said conductive element beingsubstantially unsupported against movement in said given directionexcept by its connection to said conductor ends, a member I engageablewith said conductive element, and biasing means carried by said supportand active on said member so as to urge it in said given direction so asto tend to cause said conductive element to separate from said conductorends.

2. The fuse of claim 1, in which said conductors and the conductiveelement connected thereto constitute a sub-unit insertable as such intosaid unitary structure, and means for securing said sub-unit to saidunitary structure.

3. A fuse construction comprising a housing, a pair of conductorstherein the ends of which are separated from one another, means in saidhousing for supporting said conductors against movement in a givendirection, a conductive element extending between said conductors and.connected to the ends thereof by a heat sensitive substance, saidconductive element being substantially unsupported against movement insaid given direction except by its connection to said conductor ends, asupport detachably secured to said housing and located adjacent saidconductive element, a member articulately mounted on said support andengaging said conductive element, and biasing means active on saidmember so as to urge it in said given direction so as to tend to causesaid conductive element to separate from said conductor ends.

4. In the fuse of claim 3, means operative between said member-and saidsupport preventing separation of the two under the influence of saidbiasing means.

5. The fuse of claim 3, in which said member comprises a pin slidablewith respect to said support toward and away from said conductiveelement, the tip of said pin extending in said given direction from thebody thereof and engaging said conductive element between said conductorends, said biasing means comprising a spring operatively connected tosaid pin so as to urge it toward and into engagement with saidconductive element.

6. In the fuse of claim 5, means operative between said member and saidsupport preventing separation of the two under the influence of saidbiasing means.

7. A fuse construction comprising a housing having at least one openend, a cap removably received on said open end, and a removable fuseunit within said housing, said unit comprising a pair of spacedsupports, conductors on said supports and restrained thereby againstmovement in a given direction, one end of each of said conductorsextending beyond the respective supports toward and spaced from thecorresponding end of the other conductor, terminals electricallyconnected to said conductors and extending to the exterior of saidhousing, a conductive element secured to said conductor ends betweensaid supports by a heat-sensitive substance, said conductive elementbeing substantially unsupported against movement in said given directionexcept by its connection to said conductor ends, a third supportoperatively connected to said first mentioned supports and extendingover said conductive element on the opposite side thereof from saidgiven direction, a member on said third support and engaging saidconductive element, and biasing means active on said member so as tourge it toward said conductive element so as to tend to cause saidconductive element to separate from said conductor ends.

8. The fuse construction of claim 7, in which said fuse unit isdisassemblable, said conductors and/ or conductive element beingreplaceable therein when desired.

9. The fuse of claim 8, in which said member comprises a pin slidablewith respect to said support toward and away from said conductiveelement, the tip of said pin extending in said given direction from thebody thercof and engaging said conductive element between said conductorends, said biasing means comprising a spring operatively connected tosaid pin so as to urge it toward and into engagement with saidconductive element.

10. The fuse of claim 7, in which said member comprises a pin slidablewith respect to said support toward and away from said conductiveelement, the tip of said pin extending in said given direction from thebody thereof and engaging said conductive element between said conductorends, said biasing means comprising a spring operatively connected tosaid pin so as to urge it toward and into engagement with saidconductive element.

11. The fuse construction of claim 3, in which said biasing means iscarried by said support.

12. The fuse construction of claim 3, in which said conductors, saidmeans for supporting said conductors, said conductive element and saidbiasing means are mounted on said support, thereby defining a unitarystructure removable as such from said housing.

13. The fuse construction of claim 12, in which said conductors and theconductive element connected thereto constitute a sub-unit insertable assuch into said unitary structure, and means for securing said sub-unitto said unitary structure.

14. In the fuse of claim 12, means operative between said member andsaid support preventing separation of the two under the influence ofsaid biasing means.

15. A fuse construction comprising a housing, a pair of conductorstherein the ends of which are separated from one another, means in saidhousing for supporting said conductors against movement in a givendirection, a conductive element extending between said conductors andconnected to the ends thereof by a heat sensitive substance, saidconductive element being substantially unsupported against movement insaid given direction except by its connection to said conductor ends, asupport in said housing adjacent said conductive element, a membermounted on said support and engaging said conductive element, andbiasing means active on said member so as to urge it in said givendirection so as to tend to cause said conductive element to separatefrom said conductor ends, said member comprising a pin slidable withrespect to said support toward and away from said conductive element,the tip of said pin extending in said given direction from the bodythereof and engaging said conductive element between said conductorends, said biasing means comprising a spring operatively connected tosaid pin so as to urge it toward and into engagement with saidconductive element.

16. In the fuse of claim 15, means operative between said member andsaid support preventing separation of the two under the influence ofsaid biasing means.

References Cited in the file of this patent UNITED STATES PATENTS298,121 Ross May 6, 1884 1,438,609 Perkins Dec. 12, 1922 1,685,958Sandin Oct. 2, 1928 2,239,390 Jung et al. Apr. 22, 1941 2,416,494Peterson Feb. 25, 1947 2,727,110 Von Hoorn Dec. 13, 1955 FOREIGN PATENTS147,930 Switzerland Sept. 16, 1931

